This invention pertains to the digital storage of analog information and more particularly to the digital storage of scenes in pulse coded modulated form.
In the visual arts and in particular in television or photocomposing, it is quite common to store characters, symbols, figures and the like for later transmission or printing. In many cases using television raster scanned type character generators and graphic terminals because of the grid array of the pixels and the on-off nature of the radiation beam, curved edges and edges making acute angles with the raster are jagged.
It has been found that if one amplitude modulates the intensity of the beam instead of turning it on and off, it is possible to minimize such jaggedness.
In general, the fonts of characters, symbols, etc. for the character generators are sets of digital information stored in a digital type memory. The digital information is either generated by manual techniques or by using television camera scanning of pictures or slides. Heretofore, the scanning techniques used purely binary criteria, i.e., the reflected light from a pixel of a scene was either above or below a certain value. If it were above such value a "one" or "on" was recorded in a memory cell associated with such pixel. If it was below that value a "zero" or "off" were stored. However, it was just this technique which resulted in the above-mentioned jaggedness. Thus people proposed PCM-techniques where the amplitude of the light intensity was encoded into, say, a four-bit binary number, i.e., the amplitude is quantized into sixteen levels. It is apparent that during the encoding of the information one need only feed the output of the television camera scanning the scene to an analog to digital encoder. However, because of the scanning rates, the time to perform each digital-to-analog conversion becomes extremely short. Present day digital to analog converters either cannot operate at such rates or those that can are prohibitively expensive.